Wireless soil sensor utilizing a RF frequency for performing soil measurements

Abstract

A wireless soil sensor for using a RF frequency for performing soil moisture measurements is disclosed herein. The sensor preferably includes a sensing component integrated directly with a radio and a microcontroller. The wireless soil sensor is designed to be buried underground and to transmit to above ground receivers.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]The present application claims priority to U.S. Provisional Patent Application No. 61 / 149,692, filed on Feb. 3, 2009, which is hereby incorporated by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not ApplicableBACKGROUND OF THE INVENTION[0003]1. Field of the Invention[0004]The present invention is related to a wireless sub-surface sensor having a radio for performing real-time soil measurements.[0005]2. Description of the Related Art[0006]The prior art discusses other irrigation systems and methods.[0007]Closing an underground to above ground RF communication link is a challenging task. The challenge is typically due to difficult propagation conditions perpetrated by high water content as well as high conductivity in the soil.[0008]The moisture and conductivity vary over time depending on environmental stimulus. High water content increases the rate of absorption of RF energy. Salinity and m...

AI Technical Summary

Benefits of technology

[0012]The present invention provides a solution to the problems of the prior art. The inventors of the present invention noticed the dielectric of soil, and how it changes with moisture and salinity, which led them to believe that a radiofrequency (“RF”) antenna of a wireless sub-surface soil sensor may be able to be tuned based on moisture and salinity measurements. The inventors measured soil moisture and salinity using novel sensors which also provided the electrical properties of the soil in which the wireless sub-surface soil sensor was placed. These electrical properties affect the efficient transmission and range of an antenna. The inventors realized that an antenna could be configured to optimize transmission efficiency and boost range. Components added to the antenna circuitry controlled by the processor allow for the antenna to be tuned based on the electrical properties of the soil.

[0013]RF impedances (complex resistances) are often characterized on a two dimensional SMITH® Chart. A discussion of SMITH® Charts is set forth in Designing Impedance Matching Networks With the HP 8751A, Hewlett-Packard Company, 1990, which is hereby incorporated by reference in its entirety. Another discussion of SMITH® Charts is set forth in Stephen D Stearns, Mysteries of the Smith Chart, Pacificon 2001, 2001, which is hereby incorporated by reference in its entirety. The inventors noticed that if the antenna is tuned in a specific and novel manner, its impedance is shifted in an arc around the ideal match (about 50 ohms) as moisture levels in the soil changed. By characterizing the arc by a radius and angle, the inventors were able to tune the radius to remain nearly constant. Only the phase angle of the impedance changed. The inventors designed the physical antenna structure, board structure, housing (air space) and tuning elements to maintain a constant impedance magnitude. This became an automatic, adaptive RF tuning which improved antenna performance across a range of soil moisture levels.

Problems solved by technology

Closing an underground to above ground RF communication link is a challenging task.

The challenge is typically due to difficult propagation conditions perpetrated by high water content as well as high conductivity in the soil.

However, in some instances it may not be possible to overcome the adverse effects of moisture in the ground by direct tuning of the RF and antenna components on board the underground wireless sensor.

In other instances, certain wireless sensing devices may not be able to adapt their tuning in close to real time to match the soil conditions.

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